The Dynamic Interfacial Oxygen Potential Between Iron-Carbon Droplets and Oxidizing Slag

Abstract

The dynamic nature of the interfacial oxygen potential during dephosphorization was investigated based on the concept that P O 2 at the interface between slag and liquid metal is determined by the balance between oxygen supply from reducible oxides in the slag and oxygen consumption by alloying elements in the metal. Combining this approach with the knowledge that at the phosphorus reversion point the interfacial oxygen potential can be determined from the bulk phosphorus partition ratio, the mass transfer coefficient for FeO, k FeO , was determined for different slags and found to increase with increasing FeO content. In foamy slags, k FeO was found to be a linear function of slag liquid fraction. Equating the mass transfer rate of FeO in the slag with decarburization rate, the dynamic interfacial oxygen potential was calculated over the course of the reaction, and its effect on the rate determining step for dephosphorization was evaluated.

The Influence of Sulfur on Dephosphorization Kinetics Between Bloated Metal Droplets and Slag Containing FeO

“…The observation that faster CO evolution rates decrease the phosphorus partition (Figures 2 and 5) is consistent with the authors' previous work [39] and agrees with the theory that the oxygen potential at the slag-metal interface is set by the balance between oxygen supply by the slag and oxygen consumption by carbon in the metal. [33] In apparent contradiction to this, the metal phosphorus content at the reversion point, for droplets containing 0.021 wt pct S, is much higher than at 0.007 wt pct S although the peak CO generation rates are similar.…”

“…The authors are developing a quantitative kinetic model for dynamic interfacial oxygen potential in bloated droplets, which will be presented in a subsequent publication. [42] V. CONCLUSION During reaction at 1853 K (1580°C) between Fe-C-P-S droplets and CaO-SiO 2 -Al 2 O 3 -FeO slag, decarburization was shown to go through a period of relatively slow reaction, followed by a period of very rapid reaction during which the droplet became bloated. The incubation period for bloating increased in length with the increasing sulfur content in the droplet.…”

“…This figure shows that CO generation rate increases from 5.82 9 10 À5 mole/s to a maximum of 1.04 9 10 À4 mole/s for droplets with 0.014 wt pct S. The sulfur content at the peak, 0.014 wt pct, is higher than that (0.011 wt pct) previously reported by the authors. [39] This discrepancy is believed to be related to a change in the production technique of the droplets. The mechanism by which sulfur affects decarburization behavior will be discussed in Section IV.…”

“…This work will be presented in detail in a subsequent publication. [42] For this discussion, reasonable estimates of the slag mass transfer coefficient will be used to calculate the interfacial oxygen potential as a function of droplet decarburization rate. Molloseau and Fruehan [41] investigated decarburization behavior between ironcarbon droplets and slag containing FeO and found that the value of k s is in the range of 1.3 9 10 À3 and 1.3 9 10 À2 cm/s.…”

The Effect of Sulfur Concentration in the Metal on the Mass Transfer of Phosphorus in Bloated Metal Droplets

“…Both dephosphorization and droplet residence time in the emulsion are linked to decarburization of metal droplets in different ways, complicating the reaction mechanism. Dephosphorization kinetics of bloated metal droplets have been investigated under a wide range of experimental conditions in the authors’ previous work . In that work, the authors quantified the role of CO formation, in determining the interfacial oxygen potential, as well as its contribution to mass transport of phosphorus in the metal.…”